1. Field of the Invention
The present invention relates to a band elimination dielectric filter, a dielectric duplexer, and a communication device for use in a mobile communication system for example.
2. Description of the Related Art
A conventional band elimination dielectric filter is described referring to FIG. 8 and FIG. 9.
FIG. 8 is a perspective view of a conventional band elimination dielectric filter 110, and FIG. 9 is a bottom plan view. The band elimination dielectric filter 110 comprises a dielectric resonator 120 consisting of ceramic in which two dielectric columns 122 are arranged in an intersecting manner in a cavity 121 having a conductive layer, a metallic case 130 and a base plate 140. A shield cavity comprises the metallic case 130 and the conductive cavity 121.
The metallic case 130 comprises an upper case and a lower case, but the upper case is not indicated in the figure to illustrate the inner structure in FIG. 8. An external connector 131 is for inputting/outputting the signal to/from the outside is mounted on the lower case 130. The base plate 140 is formed by providing a copper film 141 on each surface of an insulated base plate, and a strip line 142 is formed by etching a part thereof. The strip line 142 functions as a xcex/4 wavelength line, and each end thereof is connected to an internal conductor 132 of the external connector 131. In the base plate 140, the strip line 142 is arranged opposite to the lower case 130 on the upper surface side of the lower case 130 so that the strip line 142 is not brought into direct contact with the lower case 130.
One end of a loop 133 for external coupling as an external coupling means is connected to the strip line 142. The loop 133 for external coupling is extended from the base plate 140 upwardly and approximately in the perpendicular direction, while the other end of loop 133 for external coupling is connected to an etching part 143 below the base plate 140 and a copper film 141 (earth part) other than the strip line 142. Above the base plate 140, the copper film 141 in the vicinity of a penetration part of the loop 133 for external coupling is removed, and an earth plate 134 having a hole of approximately same size as that of the removed part is arranged on the base plate 140. The earth plate 134 is mounted on an inner side surface of the lower case 130, and electrically connected thereto.
In such a band elimination dielectric filter 110, the signal inputted from one external connector 131 flows in two loops 133 for external coupling and the strip line 142. The loops 133 for external coupling generate the magnetic field respectively, and the corresponding loop 133 for external coupling is respectively magnetically coupled with the dielectric column 122. Then, the signal except the frequency corresponding to the dielectric column 122 is outputted from the external connector on the output side. The band elimination dielectric filter 110 thus functions as the two-stage band elimination dielectric filter to stop the resonance frequency band specified by the size of the dielectric column 122.
The resonance frequency and the non loaded Q of the dielectric resonator are determined by the size of the cavity and the dielectric column. When the distance in the transverse direction viewed from an opening side of the dielectric resonator is defined as the xe2x80x9cwidthxe2x80x9d, the distance in the distal direction is defined as the xe2x80x9cthicknessxe2x80x9d, and the distance between the contact surfaces of the cavity and the dielectric column is defined as the xe2x80x9cheightxe2x80x9d, the following relationship is obtained.
For example, when the size of the cavity is left unchanged, and the width or the thickness of the dielectric column is increased, the resonance frequency is reduced. When the size of the dielectric column is left unchanged and the width of the cavity is increased, the resonance frequency is reduced. As for the relationship between the dielectric resonator and the non loaded Q. the non loaded Q is increased as the height of the dielectric column is increased.
As the height of the dielectric column is increased, the non loaded Q of the dielectric resonator is increased, but the cavity is also increased as the height of the dielectric column is increased. Thus, the conductive layer on the surface of the cavity is also increased in size, and the loss of the actual current flowing in the conductive layer is also increased. The loss corresponding thereto partly cancels the increase in the non loaded Q obtained by increasing the height of the dielectric column. Thus, in order to obtain the required non loaded Q, there is a concern that the dielectric resonator is increased in size. From this reason, a band elimination dielectric filter free from any loss by the actual current flowing in the conductive layer on the surface of the cavity has been desired.
In a case of a two-stage band elimination dielectric filter using a TM double mode dielectric resonator in which two dielectric columns are arranged in an intersecting manner in the cavity, two dielectric columns of the same shape are formed according to the desired resonance frequency. When the non loaded Q of the dielectric resonator is increased, the height of the dielectric column is required to be large, and the cavity is also high accordingly. Increase in the cavity by increasing the height of one dielectric column means increase in the width of the cavity when viewed from the other dielectric column. As described above, when the width of the cavity is increased, the resonance frequency is reduced, and in order to obtain the prescribed resonance frequency, the width or the thickness of the dielectric column is reduced and the resonance frequency is required to be increased. There has been a concern that the resonance frequency and the non loaded Q can not be individually designed even in the two-stage band elimination dielectric filter.
The band elimination dielectric filter of the present invention is realized in view of the above-mentioned problems, and its object is to provide a band elimination dielectric filter, a band elimination dielectric duplexer and a communication device in which the loss to be generated by the actual current flowing in the conductive layer of the cavity is eliminated, the non loaded Q is high, and the height is reduced. Another object is to provide the band elimination dielectric filter, the dielectric duplexer and the communication device in which the subordination of the resonance frequency and the non loaded Q to each other is weakened, and the resonance frequency and the non loaded Q can be individually designed.
To achieve the above-mentioned objects, the band elimination dielectric filter of the present invention includes a conductive shield cavity, a dielectric resonator which is arranged in the shield cavity and provided with electrodes formed on two surfaces opposite to each other, and an external coupling means which is arranged in the shield cavity and connected to the dielectric resonator.
The actual current flowing in the conductive layer on the surface of the cavity of the dielectric resonator is eliminated by the conventional band elimination dielectric filter, and the loss at the band elimination dielectric filter is eliminated. The corresponding non loaded Q is not canceled, the dielectric resonator need not be so high, and the height of the dielectric resonator can be reduced.
In a band elimination dielectric filter according to a second aspect of the invention, the dielectric resonator is continuously arranged in the shield cavity.
The height can be further reduced thereby.
In a band elimination dielectric filter according to a third aspect of the invention, the dielectric resonators are put on top of each other in the shield cavity.
Because the actual current flowing in the conductive layer on the surface of the cavity of the dielectric resonator is eliminated and the height is reduced compared with the conventional band elimination dielectric filter, the band elimination dielectric filter can be reduced in area.
In a band elimination dielectric filter according to a fourth aspect of the invention, at least one of electrodes formed on two surfaces opposite to each other of the dielectric resonator is formed by a thin film multilayer electrode.
The non loaded Q is further improved thereby.
A dielectric duplexer according to a fifth aspect of the invention includes at least two dielectric filters, a means for input/output connection to be connected to the respective dielectric filters, and a means for antenna connection to be commonly connected to the dielectric filter, and at least one of the dielectric filters is the band elimination dielectric filter according to first through fourth aspects of the invention.
A dielectric duplexer whose height is reduced, and whose loss is small can be provided thereby.
A communication device according to a sixth aspect of the invention includes a dielectric duplexer according to a fifth aspects of the invention, a circuit for transmission to be connected to at least one means for input/output connection of the dielectric duplexer, a circuit for reception to be connected to at least one means for input/output connection different from the means for input/output connection to be connected to the circuit for transmission, and an antenna to be connected to a means for antenna connection of the dielectric duplexer.
A communication device whose height is reduced and whose loss is small can be provided thereby.